Flashcards in DR: canine pyoderma Deck (51):
3 types of pyoderma
surface, superficial and deep
Describe surface and superficial pyodermas
epidermis only, don't penetrate below BM. typically exudative. lesions include papules, pustules, epidermal collarettes, scales, crusts, often pruritus.
Describe deep pyoderma
penetrate below BM into dermis and depper tissues, lesions include haemorrhagic bullae, nodules, ulcers, draining tracts (haemorrhagic or purulent discharge)
How is pyoderma diagnosed? 5 types?
problem-based classification based on lesion appearance:
- SEBORRHOEIC PYODERMA - erythema, erosions, exudation without pustules and collarettes
- PAPULES, PUSTULES, SCALE, FOCAL ALOPECIA
- EROSIONS and/or ULCERS
- ULCERS AND DRAINING SINUS TRACTS
- NODULES and/or REGIONAL SWELLING
Name 2 causes of seborrhoeic pyodermas - erythema, erosion, exudation without pustules and collarettes
- bacterial overgrowth syndrome
Name 3 causes of PAPULES, PUSTULES, SCALE and FOCAL ALOPECIA
- impetigo (epidermal pustules not centered on hair follicle)
- bacterial folliculitis (commonest cause of canine pyoderma)
- superficial seasonal pyoderma
Name 3 causes of EROSIONS and/or ulcers
- pyotraumatic dermatitis
- intertrigo (severe cases)
- mucocutaneous pyoderma (GSDs)
What causes the ULCERS and DRAINING SINUS TRACT form of pyoderma?
- Furunculosis (deep pyoderma) = associated with rupture of hair follicles, contents spill into dermis, creates FB reaction in dermis or subcutis. Localised or widespread
What is feline chin acne?
a type of furunculosis (i.e. depp pyoderma) with ULCERS and DRAINING SINUS TRACTS. it is a keratinisation disorder associated with comedones and furuncle formation.
What may cause the NODULE and/or REGIONAL SWELLING form of canine pyoderma?
- cellulitis (diffuse infection and inflammation along tissue planes)
What is necrostising fasciitis?
a rare but severe form of cellulitis associated with dissemination of bacterial toxins
How is pyoderma diagnosed?
- CS highly suggestive
- confirmed with cytology
- and where necessary bacterial culture and AB sensitivity
What are the 4 main cytological techniques for diagnosing canine pyoderma?
- adhesive tape strip cytology
- direct impression smears
- indirect impression smears
- needle cores and FNAs
What is adhesive tape strip cytology good for?
- removes outer SC layer and adherent microorganisms
- sample dry, greasy, scaling or eroded lesions
- irregular surfaces or restricted sites
When are impression smears useful?
- moist or seborrhoiec lesions
- direct - erosion, crust underside or ruptured pustule
- indirect - when slide cannot be apposed to skin and adhesive tape strips are unsuitable (use cotton bud etc)
When are needle cores useful?
- cutaneous massess and enlarged LNs
How are cytology samples stained?
- Diff-Quik (inflammatory cells and microorganisms
- heat fixation not necessary
- Gram and Ziehl-Nielsen (more precisely ID bacteria_
Describe inflammatory cells in canine pyoderma
- neutrophils predominate in most cases
- degenerate/toxic indicate infection
- non-degenerate (sterile inflammation)
- both may be seen
- macrophages + microorganisms, degnerate cells, other debris suggest chronic and/or deep pyoderma
- many macrophages or MNGCs - mycobacterial or fungal infection
- most inflammatory reactions have moderate lymphocytes, PCs and eosinophils - little diagnostic significance
What is bacterial overgrowth like on cytology?
large numbers of bacteria, often several different forms, with no or only minimal numbers of inflammatory cells
Is the presence of intracytoplasmic bacteria a definite indicator of infection?
Name common rod bacteria
Psuedomonas, Proteus and coliforms
What are potential mistakes in cytology interpretation?
- representative lesions
- don't make diagnosis on signle finding
- positive findings useful
- negative results interpreted with case
When is empirical AB therapy appropriate?
WHEN ALL OF FOLLOWING APPLY:
- non-life threatening infection
- 1st episode of skin infection
- lesions consistent with surface/superficial pyoderma
- cytology consistent with staph infection
- no reason to suspect AB resistance
When is bacterial C+S appropriate?
WHEN ANY OF THE FOLLOWING APPLY:
- life threatening infections
- clinical lesions consistent with deep pyoderma
- CS and cytology not consistent with each other
- rod bacteria seen on cytology (their AB sensitivity is not predictable and may be limited)
- empirical AB tx doesn't resolve infection
- where AB resistance more likely (after one or more BS AB courses, non-healing wounds, postop and other nosocomial infections OR the owner or animal has recent healthcare contacts)
Does cytology or culture yield quantitative data?
cytology - also informs of whether organisms have been phagocytosed and relationship to cutaneous cells and structures
When should you take a sample for cytology if ABs have already been used?
48 hours after last dose of oral ABs or beyond appropriate dose interval for parenteral ABs. If not possible use prolonged and/or enriched cultures
What are the best bacteriology swabs for routine clinical use?
standard cotton tipped swabs in transport medium for aerobic and anaerobic growhth
When are biopsies preferred to swabs?
for deeper lesions as bacteria on skin surface may not be representative of deeper organisms
- local anaesthesia may be bactericidal so may be better to use a ring block, local nn block or GA
What is the proper name for disc diffusion test culture?
Kirby-Bauer disc diffusion tests (use AB impregnated discs) - .n.b. some disc diffusion tests may give misleading results for susceptibility in vitro versus in vivo
How should a bacteria be regarded if it is described as having intermediate sensitivity to an AB?
best regarded as resistant
Define MIC. How is it determined?
- Minimum Inhibitory Concentration = the lowest concentration of an AB that completely inhibits the growth of a microorganism
- DETERMINATION: various methods, broth dilution methods that culture a known quantity of bacteria with doubling dilutions of AB are most common.
What are additional tests that may be necessary to confirm the ID, characteristics and antimicrobial susceptibility of bacterial isolates?
- PBP2a latex bead agglutinations tests
- mecA PCR and SCC mec typing for MRS
- PCR for extended-spectrum beta-lactamase (ESBL) E.coli
Do you treat pyoderma with systemic or topical tx?
- Mild, surface and/or focal infections - topical AM shampoos and sprays or even topical ABs if topical antiseptics don't clear infection. Topical antiseptic treatments can hasten clearing the infection or will greatly reduce the need for systemic therapy.
- Deep, severe, generalised - systemic ABs
What are the most relevant points when considering systemic AB tx for pyoderma?
- mostly coagulase-positive staph
- skin is largest organ of body, poor blood supply
- length of tx depends on depth of infection
- most cases are secondary to other pathologies which must be addressed to obtain a clinical cure
- using topical antiseptic tx will hasten clearing the infection
What are first line ABs for pydoerma?
- (cefpodoxine and cefovecin when medication or compliance likely to be poor)
What first line ABs are staph resistant to?
TCs and simple penicillins
When should second-line ABs be used?
only when there is culture evidence that first-line drugs will not be effective
List second-line ABs
newer BS ABs important to health including cefovecin, cefopodoxime (both used as first line sometimes), difloxacin, enrofloxacin, marbofloxacin, orbifloxacin and pradofloxacin
When can third-line ABs be used for pyoderma?
only where there is C+S evidence that no 1st or 2nd line ABs are effective and that topical AMs tx is not feasible or effective
List third-line ABs
aminoglycosides, azithromycin, ceftazamidine, chloramphenicol, clarithromycin, florphenicol, imipenum, phosphomycin, pueracillin, rifampin, tiamphenicol and ticarcillin
When should pyoderma tx start?
- ideally not until C+S results are back
- if immediate tx necessary, select an appropriate drug based on CS, ctyology, most likely organisms and likely AM sensitivity
What sort of AB dose should be used?
upper end of dose range as skin is the largest organ of the body and its blood supply is comparatively poor. Always weigh an animal first. If necessary slightly overdose - never underdose
How long is AB tx needed?
SUPERFICIAL - typically 2-3 weeks
DEEP - greatly improved after 2 weeks, full resolution often takes 4-6 weeks longer
- continue until infection is visually and palpably cured and cytology is normal - traditional to continue tx for another 7d (superficial) or 14 d (deep) but largely anecdotal evidence
How can owner compliance be improved?
- long duration injectable drugs
- once daily drugs
- palatable drugs
- owner can administer safely
- convincing owner
- written instructions
- precise terminology
- good follow up and communication
- minimising the number of different drugs or tx
- warn of common and mild adverse effect (GIT upsets)
What do adverse effects arise from? 3
- effect on non-target bacteria
- pharmacological activity
- immune-mediated drug reactions
What are examples of underlying primary diseases for canine pyoderma?
hypersensitivity, ectoparasitic infestation, endocrinopathy, keratinisation defects
Why might there be poor penetration to deep pyoderma?
deep pyodermas often feature extensive necrosis, scarring and debirs that may limit penetration and acitivity of some ABs. Clindamycin, cefovecin and fluoroquinolones penetrate well to sites of skin infection and inflammation and could be used in these cases.
What may cause poor response to AB tx for pyoderma? 6
- midiagnosis of bacterial skin infection
- resistant organisms
- incorrect AB administration
- incorrect AB dose and duration
- concurrent inappropriate use of immunosuppressive drugs (esp GCs)
- poor distribution to target tissue
Causes - recurrent pyoderma
- RELAPSE AFTER A FEW DAYS - the AB course was too short so give a longer course (following C+S)
- RELAPSES WEEKS OR MONTHS AFTER AB WITHDRAWAL - there is probably an undiagnosed or uncontrolled underlying cause.
- occasionally no underlying cause can be found (primary pyoderma) or cannot be controlled. Use immunostimulants or autogenous bacterial vaccines.